Drive Flank Engagement Between Rotating Components and Shaft of Electrical Submersible Well Pump

ABSTRACT

A well pump has a shaft with at least one shaft drive flank extending a length of the shaft. Impellers are located between non-rotating diffusers. Each impeller has a hub with an impeller hub bore through which the shaft extends. The impeller hub bore has at least one impeller drive flank that is in flush contact with the shaft drive flank to impart rotation to the impeller. The shaft drive flanks may be on opposite sides of the shaft and parallel with each other. The shaft may have six of the shaft drive flanks symmetrically arranged around the shaft and joining each other. The shaft drive flanks may be three involute curved surfaces that join each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional application 62/678,313filed May 31, 2018.

BACKGROUND

One type of submersible well fluid pump has an electrical motoroperatively connected with a centrifugal pump. The pump has a largenumber of stages, each stage having an impeller and a diffuser. A shaftrotated by the motor rotates the impellers relative to the diffusers.Each impeller has passages that lead upward and outward to the nextupward diffuser. Each diffuser has passages that extend upward andinward to the next upward impeller.

The impellers and the shaft have mating keyway slots in which a key ispositioned to lock the impellers to the shaft for rotation. Whilesuccessful, during operation, sand from the well fluid flowing throughthe pump may accumulate in the keyway slots, creating problems.

SUMMARY

A well pump assembly comprises a pump having a housing with alongitudinal axis. A shaft extends through the housing on the axis, theshaft having at least one shaft drive flank integrally formed thereonand extending substantially a length of the shaft. A plurality ofdiffusers are fixed in the housing against rotation, each of thediffusers having diffuser passages extending from a diffuser inlet to adiffuser outlet. Each of the diffusers has a diffuser bore through whichthe shaft extends. An impeller is located between each of the diffusers.The impeller has impeller passages extending from an impeller inlet toan impeller outlet. The impeller has an impeller hub with an impellerhub bore through which the shaft extends. The impeller hub bore has atleast one impeller drive flank integrally formed therein that is inflush contact with the shaft drive flank to impart rotation to theimpeller.

In some embodiments, the at least one shaft drive flank comprises aplurality of shaft drive flanks symmetrically arranged around anexterior of the shaft. In one embodiment, the at least one shaft driveflank comprises two of the shaft drive flanks on opposite sides of theshaft and parallel with each other. In another embodiment, the at leastone impeller drive flank comprises at least six of the impeller driveflanks symmetrically arranged around the impeller hub bore and joiningeach other. In still another embodiment, the at least one impeller driveflank comprises three involute curved surfaces that join each other. Theat least one impeller drive flank may comprise a single flat surfaceasymmetrically formed in the impeller hub bore.

The pump may have spacer rings through which the shaft extends. Thespacer rings are positioned between and in abutment with the impellerhub. Each of the spacer rings has a bore through which the shaft passes.The bore in the each of the spacer rings has at least one spacer ringdrive flank that mates with the shaft drive flank.

The pump may have a shaft coupling on a driven end of the shaft. Theshaft coupling has a coupling bore with at least one coupling driveflank that mates with the shaft drive flank.

An exterior of the impeller hub is cylindrical and in rotating, slidingcontact with the diffuser bore in one of the diffusers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an electrical submersible pumpassembly in accordance with this disclosure.

FIG. 2 is a sectional view of a portion of the pump of FIG. 1.

FIG. 3 is a sectional view of the shaft and a coupling of the pump ofFIG. 2, taken along the line 3-3 of FIG. 2.

FIG. 4 is an perspective view from an upper side of one of the impellersof the pump of FIG. 1, shown removed from the pump.

FIG. 5 is a top view of the impeller of FIG. 4.

FIG. 6 is top view of an alternate embodiment of the impeller of FIG. 4.

FIG. 7 is a transverse sectional view of the hub of an alternateembodiment of one of the impellers of FIGS. 2 and 4.

FIG. 8 is a perspective view of a portion of the impeller hub of FIG. 7.

FIG. 9 is a transverse sectional view of the hub of another alternateembodiment of the impellers of FIGS. 2 and 4.

FIG. 10 is a perspective view of a portion of the impeller hub of FIG.9.

While the disclosure will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit thedisclosure to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION OF THE DISCLOSURE

The method and system of the present disclosure will now be describedmore fully hereinafter with reference to the accompanying drawings inwhich embodiments are shown. The method and system of the presentdisclosure may be in many different forms and should not be construed aslimited to the illustrated embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey its scope to those skilled in the art.Like numbers refer to like elements throughout. In an embodiment, usageof the term “about” includes +/−5% of the cited magnitude. In anembodiment, usage of the term “substantially” includes +/−5% of thecited magnitude.

It is to be further understood that the scope of the present disclosureis not limited to the exact details of construction, operation, exactmaterials, or embodiments shown and described, as modifications andequivalents will be apparent to one skilled in the art. In the drawingsand specification, there have been disclosed illustrative embodimentsand, although specific terms are employed, they are used in a genericand descriptive sense only and not for the purpose of limitation.

Referring to FIG. 1, a well with casing 11 is illustrated as containingan electrical submersible pump assembly (ESP) 13. ESP 13 has a motor 15,which is normally a three phase electrical motor. Motor 15 is filledwith a dielectric motor lubricant. A pressure equalizer or seal section17 has features to equalize the internal pressure of the motor lubricantwith the hydrostatic pressure of well fluid surrounding motor 15. Sealsection 17 may be located above motor 15, as shown, and will be in fluidcommunication with the motor lubricant in motor 15. Alternately, apressure equalizer could be located below motor 15. Motor 15 has a driveshaft assembly that extends through seal section 17 and drives acentrifugal pump 19, which has an intake 21 for drawing well fluid in.

A string of production tubing 23 extends to a wellhead (not shown) andsupports ESP 13. Tubing 23 may comprise sections secured together bythreads. Alternately, tubing 23 may comprise continuous coiled tubing. Apower cable 25 extends downward from the wellhead and is strapped totubing 23. A motor lead 27 connects to power cable 25 at a splice orconnection 29 located above ESP 13. Motor lead 27 extends alongside ESP13 and has a motor lead connector 31 on its lower end that plugs into areceptacle at the upper end of motor 15. Pump 19 discharges well fluidthrough its upper end into tubing 23 in this example. If tubing 23 iscontinuous coiled tubing, power cable 25 could be located inside thecoiled tubing, in which case, pump 19 would discharge into an annulussurrounding the coiled tubing.

Motor 15, pump 19 and seal section 17 comprise modules that are broughtseparately to a well site, then secured together by bolted flanges orthreaded collars. ESP 13 may have other modules, such as a gas separatorand a thrust bearing unit. Alternately, a thrust bearing unit could beformed as part of seal section 17. Also, motor 15, pump 19 and sealsection 17 each could be formed in more than one module and connected intandem.

Referring to FIG. 2, pump 19 has a tubular housing 33 with a cylindricalinner side wall concentric with a longitudinal axis 35. A steel driveshaft 37 extends through housing 33 concentric with axis 35. Shaft 37can be lengthy; for example, shaft 37 may be 20-30 feet in length.Referring to FIG. 3, shaft 37 has an exterior surface with cylindricalportions 39 joined by drive flanks 41, which in this example comprisestwo. Drive flanks 41 are flat surfaces parallel with each other and onopposite sides of shaft 37 that are integrally formed in the cylindricalexterior surface 39. Drive flanks 41 may vary in width, and in thisexample, each drive flank has a width from one side edge to another ofabout half the diameter of shaft 37 measured between cylindricalportions 39. Cylindrical portions 39 are on opposite sides of shaft 37and have the same diameters.

Positioning drive flanks 41 on opposite sides of shaft 37 and parallelto each other makes drive shaft 37 symmetrical, reducing vibration. Aline 42 normal to one of the drive flanks 41 and at a midpoint betweenthe side edges of the drive flank 41 passes through axis 35 and throughthe midpoint of the opposite drive flank 41. Similarly, a line normal tothe midpoint of one of the cylindrical portions 39 passes through axis35 and through the midpoint of the opposite cylindrical portion 39.Drive flanks 41 are formed in one method by machining a cylindricalshaft.

Drive flanks 41 extend substantially the length of the shaft. In thisexample, drive flanks 41 extend continuously to at least one end ofshaft 37, such as the lower end. A coupling 43 slides over the lower endof shaft 37 and couples shaft 37 to another shaft 46, such as shaft 46of seal section 17, which in turn is driven by the shaft of motor 15(FIG. 1). Shaft 46 may be considered to be a motor shaft or a drivingshaft. The lower end of shaft 37 may be considered to be the driven endof shaft 37.

In this example, at least the upper half of coupling 43 has a couplingbore 45 with two cylindrical portions 45 a joined by two drive flanks 45b. The dimensions of coupling bore 45 mate with drive shaft 37 to causedrive shaft 37 to rotate in unison. Coupling bore drive flanks 45 b havethe same dimensions as shaft drive flanks 41, and coupling borecylindrical portions 45 a have the same dimension as shaft cylindricalportions 39, within close tolerances. Coupling 43 has a wall thicknessmeasured from bore 45 to the cylindrical exterior surface. The wallthickness is uniform where measured from the cylindrical portion of bore45 to the exterior. The wall thickness from the cylindrical exterior toone of the coupling drive flanks 45 b increases from the side edges ofthe drive flank 45 b to a greatest thickness at the midpoint whereintersected by line 42.

Shaft 46 within seal section 19 (FIG. 1) may have an upper end withdrive flanks in the same manner as pump shaft 37 for sliding into alower portion of coupling 43. Alternatively, the upper end of sealsection shaft 46 could be splined with conventional triangular splines.If splined, the lower portion of coupling bore 45 would have matingsplines.

In this example, the upper end of pump shaft 37 is not coupled to ashaft in another module. The exterior of shaft 37 at the upper end couldbe completely cylindrical, or it could have splines or it could havedrive flanks 41. In the case of a tandem pump (not shown) mounted abovepump 19, the upper end of drive shaft 37 could utilize drive flanks 41.If so, an upper drive shaft coupling with drive flanks similar tocoupling 43 could be employed on the upper end of pump shaft 37.

A stack of diffusers 47 (only two shown) fits closely in housing 33 fornon-rotation. Diffusers 47 may be identical, each having a centralcoaxial diffuser bore 49 through which drive shaft 37 extends but doesnot contact. Each diffuser bore 49 is cylindrical. Each diffuser 37 hasdiffuser passages 51 that extend from a lower inlet upward and radiallyinward to an upper outlet.

An impeller 53 (only one shown) mounts between each of the diffusers 47.Impeller 53 has impeller passages 55 that extend upward and outward froma lower inlet to an upper outlet. Impeller 53 has a cylindrical hub 57extending upward and outward into diffuser bore 49 of the next upwarddiffuser 47. Impeller 53 has an impeller bore 59 extending from itslower side to its upper side through which shaft 37 extends.

Referring to FIGS. 4 and 5, in this embodiment, impeller bore 59 has twocylindrical portions 59 a joined by two flat drive flanks 59 b.Cylindrical portions 59 a and drive flanks 59 b are dimensioned to mateand be in flush contact with shaft drive flanks 41, within closetolerances. Shaft drive flanks 41 cause impeller 53 to rotate in unison.Although is a sectional view of coupling 43, it also represents theengagement of shaft drive flats 41 with impeller drive flanks 59 b.Other than impeller bore 59, the remaining configuration of impeller 53may be conventional. The discussion of the features of drive flanks 45 bin coupling 43 also applies to impeller drive flanks 59 b.

Spacer rings 61 encircle shaft 37 and are located between impellers 53.Spacer rings 61 abut the upper end of the hub 57 of a next lowerimpeller 53 and the lower side of the next upward impeller 53. Eachspacer ring 61 rotates with shaft 37 and has a bore 63 with drive flanksthat mate with drive flanks 41 of shaft 37. The cross-section of one ofthe spacer rings 61 would appear to be the same as the cross-section ofcoupling 43 of FIG. 3. The discussion above of the features of couplingdrive flanks 45 b also applies to the drive flanks in spacer ring 61.

During assembly, a technician alternates sliding each diffuser 47 overshaft 35 with sliding one of the impellers 53 and one or more of thespacer rings 61. If the lower end of shaft 37 is the only end havingdrive flanks 41, the technician would slide the diffusers 47, impellers53 and spacer rings 61 over the lower end.

Impellers 53 are free to slide upward and downward short distances ondrive shaft 37 between down thrust and up thrust conditions. In the upthrust conditions, an upper side portion of impeller 53 abuts a thrustwasher on the lower side of the next upward diffuser 47. In the downthrust condition, a lower side portion of impeller 53 abuts a thrustwasher on an upper side of the next downward diffuser 47. Shaft driveflanks 41 can also cause impellers 53 to spin shaft 37 in reverserotation due to a falling column of well fluid in production tubing 23in the event motor 15 shuts off.

In many well installations, motor 15 (FIG. 1) is operated at a fixedspeed that is typically about 3600 rotations per minute (RPM).Alternately, a variable speed drive near the wellhead (not shown) maychange the rotational speed of the motor from less than 3600 RPM tomore.

Impellers 53 may be constructed of conventional materials, such as acasting of a nickel iron alloy. The dimensions of impeller bore 59 canbe finalized by broaching.

Referring to alternate embodiment of FIG. 6, impeller 65 has a bore 67with more than two drive flanks 69. In this example, there are six driveflanks 69, but the number could be more or less. Bore 67 has nocylindrical portions. Drive flanks 69 are flat surfaces with edgesjoining each other at 120 degree included angles to define a hexagonalconfiguration for bore 67. As in FIG. 3, a line (not shown) normal toeach drive flank 69 at its midpoint will pass through the axis ofrotation. The exterior of the hub of impeller 65 is cylindrical, thusthe wall thickness measured from drive flanks 69 to the cylindricalexterior will change. The thickest portion of the wall of the hub ofimpeller 65 will be at the midpoint between side edges of each driveflank 69. The thinnest wall thickness portion will be at the side edgesof each impeller drive flank 69.

Drive shaft 37 (FIG. 2) will have a mating hexagonal configuration thatclosely receives each impeller 65. A hexagonal exterior for drive shaft37 is also symmetrical, reducing vibration. Other than having hexagonaldrive flanks 69, impeller 65 may be the same as impellers 53.

FIGS. 7 and 8 illustrate another embodiment of an impeller hub 71. FIGS.7 and 8 do not show the remaining portions of the impeller of hub 71,but they may be the same as impeller 53 (FIGS. 2 and 4). Impeller hub 71has three internal drive flanks 73 with side edges that join each other.Each drive flank 73 is a curved involute surface with a separate radialcenter point 75 offset from axis 77 of rotation. Each curved flank 73 isformed with a radius 79 extending from a radial center point 75. Radius79 has a greater length than a radial line extending from rotationalaxis 77 to any part of any of the impeller drive flanks 73. The radialcenter point 75 for each drive flank 73 will be at a different locationfrom the radial center points of the other drive flanks 73. A line 80normal to each drive flank 73 at a midpoint between the side edges ofeach drive flank 73 will pass through axis 77.

The drive shaft (not shown) for impeller hub 71 will have curvedinvolute drive flanks on its exterior surface that mates in flushcontact with drive flanks 73. The curved drive flanks on the drive shaftextend substantially a full length of the drive shaft in the same manneras drive flats 41 (FIG. 3). Spacer rings (not shown) similar to spacerrings 61 (FIG. 2) would have similar internal curved drive flanks intheir bores. A coupling similar to coupling 43 (FIG. 2) could havesimilar internal drive flanks in its bore, at least in the portion thatslides over the lower end of the drive shaft.

FIGS. 9 and 10 illustrate still another embodiment of an impeller hub81. FIGS. 9 and 10 do not show the remaining portions of the impeller ofhub 71, but they would be the same as impeller 53 (FIGS. 2 and 4).Impeller hub 81 has a cylindrical bore 83 with a single flat drive flank85 formed in it, generally defining a D-shaped configuration. Driveflank 85 has a width from one side edge to another side edge that mayvary, and in this example, the width of drive flank 85 is about half theinner diameter of hub bore 83, measured through the axis betweencylindrical portions of bore 83. Drive flank 85 may be configured thesame as one of the drive flanks 45 b of FIG. 3. As there is only onedrive flank 85, impeller hub bore 83 is asymmetrical.

A drive shaft for impeller hub 81 will have only a single drive flank onits exterior surface that mates with drive flank 95. The single driveflank on the drive shaft may extend a full length of the drive shaft inthe same manner as the two drive flats 41 of FIG. 3. Spacer rings wouldhave a similar single flat drive flank. Optionally, a coupling couldhave a similar single, flat drive flank, at least in the portion thatslides over the lower end of the drive shaft.

A pump designer when designing a pump with drive flanks will considerthe allowable torque. The designer will perform a stress calculationusing finite element analysis. The designer will consider wear on theshaft and the bores of the rotating components. The designer must alsoconsider stage vibration. Further, the designer will consider thedifficulty of manufacturing the shaft and rotating components as well asthe assembly.

The present disclosure described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a few embodiments of thedisclosure have been given for purposes of disclosure, numerous changesexist in the details of procedures for accomplishing the desiredresults. These and other similar modifications will readily suggestthemselves to those skilled in the art, and are intended to beencompassed within the scope of the claims.

1. A well pump assembly, comprising: a pump having a housing with alongitudinal axis; a shaft extending through the housing on the axis,the shaft having at least one shaft drive flank integrally formedthereon and extending substantially a length of the shaft; a pluralityof diffusers fixed in the housing against rotation, each of thediffusers having diffuser passages extending from a diffuser inlet to adiffuser outlet, each of the diffusers having a diffuser bore throughwhich the shaft extends; and an impeller located between each of thediffusers, the impeller having impeller passages extending from animpeller inlet to an impeller outlet, the impeller having an impellerhub with an impeller hub bore through which the shaft extends, theimpeller hub bore having at least one impeller drive flank integrallyformed therein that is in flush contact with the shaft drive flank toimpart rotation to the impeller.
 2. The pump assembly according to claim1, wherein the at least one shaft drive flank comprises a plurality ofshaft drive flanks symmetrically arranged around an exterior of theshaft.
 3. The pump assembly according to claim 1, wherein the at leastone shaft drive flank comprises two of the shaft drive flanks onopposite sides of the shaft and parallel with each other.
 4. The pumpassembly according to claim 1, wherein the at least one impeller driveflank comprises at least six of the impeller drive flanks symmetricallyarranged around the impeller hub bore and joining each other.
 5. Thepump assembly according to claim 1, wherein the at least one impellerdrive flank comprises three involute curved surfaces that join eachother.
 6. The pump assembly according to claim 1, wherein the at leastone impeller drive flank comprises a single flat surface asymmetricallyformed in the impeller hub bore.
 7. The pump assembly according to claim1, further comprising: spacer rings through which the shaft extends, thespacer rings being positioned between and in abutment with the impellerhub, each of the spacer rings having a bore through which the shaftpasses, the bore in the each of the spacer rings having at least onespacer ring drive flank that mates with the shaft drive flank.
 8. Thepump assembly according to claim 1, further comprising: a shaft couplingon a driven end of the shaft, the shaft coupling having a coupling borewith at least one coupling drive flank that mates with the shaft driveflank.
 9. The pump assembly according to claim 1, wherein: an exteriorof the impeller hub is cylindrical and in rotating, sliding contact withthe diffuser bore in one of the diffusers.
 10. A well pump assembly,comprising: a pump having a housing with a longitudinal axis; a shaftextending through the housing on the axis, the shaft having at least oneshaft drive flank extending substantially a length of the shaft, whereina line normal to a midpoint of the shaft drive flank passes through theaxis; a plurality of diffusers fixed in the housing against rotation,each of the diffusers having diffuser passages extending from a diffuserinlet to a diffuser outlet, each of the diffusers having a diffuser borethrough which the shaft passes but does not contact; and an impellerlocated between each of the diffusers, the impeller having impellerpassages extending from an impeller inlet to an impeller outlet, theimpeller having an impeller hub with an impeller hub bore through whichthe shaft extends, the impeller hub bore having at least one impellerdrive flank integrally formed therein that mates with the shaft driveflank to impart rotation to the impeller, wherein a line normal to amidpoint of the impeller drive flank passes through the axis.
 11. Thepump assembly according to claim 10, wherein: the impeller hub has acylindrical exterior with a wall thickness measured between the impellerdrive flank and the cylindrical exterior; the wall thickness between theimpeller drive flank and the cylindrical exterior is greatest at themidpoint of the impeller drive flank; and the wall thickness between theimpeller drive flank and the cylindrical exterior is least at ends ofthe impeller drive flank.
 12. The pump assembly according to claim 10,wherein the at least one impeller drive flank comprises two flatsurfaces formed on opposite sides of the impeller hub bore, the flatsurfaces being parallel with each other.
 13. The pump assembly accordingto claim 10, wherein the at least one impeller drive flank comprises sixflat surfaces, defining a hexagonal configuration for the impeller hubbore.
 15. The pump assembly according to claim 10, wherein: the at leastone impeller drive flank comprises three involute, curved surfacesformed in the impeller hub bore; and each of the curved surfaces has aradial center point that is offset from the axis.
 16. The pump assemblyaccording to claim 10, wherein the impeller drive flank comprises asingle flat surface formed on one side of the impeller hub bore.
 17. Awell pump assembly, comprising: a pump having a housing with alongitudinal axis; a shaft extending through the housing on the axis,the shaft having a plurality of shaft drive flanks extendingsubstantially a length of the shaft and symmetrically arranged aroundthe shaft; a plurality of diffusers fixed in the housing againstrotation, each of the diffusers having diffuser passages extending froma diffuser inlet to a diffuser outlet, each of the diffusers having adiffuser bore through which the shaft passes but does not contact; and aplurality of impellers, each of the impellers being located between eachof the diffusers, each of the impellers having impeller passagesextending from an impeller inlet to an impeller outlet, each of theimpellers having an impeller hub with an impeller hub bore through whichthe shaft extends, the impeller hub bore having a plurality of impellerdrive flanks, each of the impeller drive flanks being in flush contactwith one of the shaft drive flanks.
 18. The pump assembly according toclaim 17, wherein: the shaft drive flanks are flat, on opposite sides ofthe shaft and parallel with each other.
 19. The pump assembly accordingto claim 17, wherein the shaft drive flanks comprise six flat surfacessymmetrically arranged around the shaft and joining each other.
 20. Thepump assembly according to claim 17, wherein the shaft drive flankscomprise three involute curved surfaces that join each other.